Electronic devices are moving to higher frequencies. In line with this, capacitors, which are often used in power supply circuits and digital signal processing circuits as an electronic component, have been required to have excellent impedance characteristics at higher frequencies than before. In order to meet this demand, various solid electrolytic capacitors with solid electrolyte made of highly electric conductive polymer have been suggested.
FIG. 9 is a sectional view of a conventional solid electrolytic capacitor. FIG. 10 is a perspective view of the capacitor, and FIG. 11 is a partially cutaway perspective view of a capacitor element used in the capacitor. Capacitor element 20 includes anode portion 23 and cathode portion 24 which are formed on anode body 21. Anode body 21 is made of aluminum foil, which is a valve metal. Anode body 21 is divided into anode portion 23 and cathode portion 24 by first forming a dielectric oxide film layer on its surface and then being provided with insulating resist portion 22. Cathode portion 24 is provided on its surface with solid electrolyte layer 25 and cathode layer 26 laminated in this order. Cathode layer 26 is made of carbon and silver paste.
Anode portion 23 is mounted on the connecting face of anode terminal 27 and cathode portion 24 is mounted on the connecting face of cathode terminal 28, respectively. The connecting face of cathode terminal 28 is partly bent up to form guide portions 28A. A node portion 23 is resistance-welded to connecting portion 27A, which is formed by bending the connecting face of anode terminal 27. Cathode portion 24 is connected to the connecting face of cathode terminal 28 with unillustrated conductive silver paste.
Insulating coating resin 29 covers capacitor element 20 so as to expose part of anode terminal 27 and part of cathode terminal 28 which are connected to capacitor element 20 in this manner. Anode terminal 27 and cathode terminal 28 exposed from coating resin 29 are extended along the side surfaces and bent to the bottom surface of coating resin 29 so as to form external terminals. In this manner, a surface-mount-type solid electrolytic capacitor is structured. One such solid electrolytic capacitor is disclosed in Japanese Patent Unexamined Publication No. 2000-340463.
In the aforementioned conventional solid electrolytic capacitor, however, anode terminal 27 and cathode terminal 28 are so complicated in shape that it increases the cost of the capacitor. In addition, anode terminal 27 and cathode terminal 28 have a long distance between their connecting faces to which capacitor element 20 is connected and their mounting sides so as to increase ESL (equivalent series inductance) of the solid electrolytic capacitor.
In recent years, there is a high demand for reduction in size and increase in capacity of electrolytic capacitors used around the CPU in personal computers or in driving power supply circuits, switching power supply circuits, and the like. Furthermore, as the electrolytic capacitors are moving to higher frequencies, lower ESL is demanded to achieve excellent noise reduction and transient response as well as lower ESR (equivalent series resistance). The aforementioned conventional solid electrolytic capacitor, however, does not satisfy these requirements.
In order to satisfy the requirements, there have been suggested a solid electrolytic capacitor that has a shorter distance from the capacitor element to the mounting side. An example of such a solid electrolytic capacitor is shown in FIG. 12A as a cross section.
In capacitor element 41, anode lead 42 is connected to anode lead frame 43 and the cathode side thereof is connected to cathode lead frame 44. These connected areas and the whole of capacitor element 41 are coated with resin 45. The solid electrolytic capacitor is surf ace-mounted on circuit board 46. Anode lead frame 43 and cathode lead frame 44 that also function as external terminals are designed to have distance 47 of not more than 3 mm. Setting distance 47 between both electrodes to not more than 3 mm can reduce ESR and ESL of the solid electrolytic capacitor.
This solid electrolytic capacitor, however, has air tightness level not satisfying commercial requirements.